Method of extracting uranium values from uranium bearing material



United States atenlti'p'V METHOD oF EXTRACTING URANIUM VALUES FROM URANIUM BEARING MATERIAL No` Drawing. Application November 7, 1955 Serial N; 545,545

Claims.l (Cl. 23-14.5)

This invention relates to a method of separating urani" um values from copper values` in.` the recovery of uranium values from uraniumy bearing material such as ores, concentrates, metallurgical residues,A intermediates, by-prodf usts andthe like which contain copper values in addition to uranium values.

, This application is a continuation-impart of our ap, plication No. 462116, liled Getober 13, 1954, nowv Patent No. 2,797,977, issued July 2,` 1957.

Uranium usually is found in nature as an oxide, such=V as'pi'tchblend'e, U3O8, or a phosphate such as torbernite, metatorbernite and autunite or associated with values of other metals such as Withi vanadium as carnotite, a uranium vanadate.: Uranium maybe andV frequently i's associated in ore-` deposits` and in uranium bearing by'-` products metallurgical; inter-mediates and residues with` values of, other minerals; such: as copper, from" which the. uranium must be separated: to` produce a: uranium;v product-tsuitable for laboratory and commercial use;

It. is knownz that, uraniumv can be extractedf tromA uta-- nium bearing materials; by1 leaching `the materiali with aA dilute sulphuric acida solution' in'` a closed reaction vess'e'l maintained au elevated temperature and under a positive partialipressureio'oxygen, such as` produced byf feeding aus oxygenbearing,l oxidizing gas into the reaction-VesselV during the: course: of thei leachingoperation.V g

This: acidleaching'method", which isJ described' in: detail1k inioun co-pending application, Serial No.- 462,116', filedV October 133;, 1954,. hasl the important advantage* that' uranium` values. arerapidly extracted from the uranium bearing'material andI dissolved in the leachV solution` with, a. high Vdegree off extractive` etliciency; However, when' acid* leaching-f isv employed* to recover uranium values from copper'bearingl ores, the presence of copper re'sults in excessive'. consumption of precipitation reagents andy makes-it; ditlicult to recover' aV high grade uranium prodi uct-ifr'om theleach'solution: At least part of the' copper values tendE to dissolveY in theV leach solution and part remains in the residue. The residue can be treated separately; iff desired, for the recovery of copper' values. Separation" of' dissolved copper values froml the lacli` solution, Whicli contains' dissolved uranium values can, beeif'ectedi such"as'byfcementation. For example,.cop percanbe precipitated* from dilute acid solution by the addition of iron, such as in the form of" sheet m'etal'. However; such precipitation' methods are complicated and costly'andjalso; may constitute a source of loss ofuranium' values; p

We have-foundthat`th`e problem ofthe presence of copper'v-alues'witll" uraniumvalues inluranium bearing material can'be overcorn'einm a surprisingly simple but highly etfctive manner. In general; the method ofthelpresent. inventionof` separating` copper values from uranium: values? comprises tliefstep of. digestingyatra temperaturer above. atmospheric. temperature, `in the presence of -urn dissolved. residuer from.- thel leaching` stepl andYA iront..l sulphide; an, aqueous;I acidjsulphate solutionA containing;

Y 2v in solution, uranium valuesand copper values, and continuing the digestingl for a period of time suliicient to precipitate copper values from the solution.

The method of the present invention is independent of the source or origin of the aqueous acid sulphate solution` whic-hcontains the dissolved uranium and Ycopper values. However, a preferred method of obtaining the solution, and which forms a feature of this invention,

comprises the steps ofl forming a` slurry` of finely divided uranium bearing material containing copper values,`

iron sulphide and an' aqueous solution of the group consisting of water and aqueousl acid solution.- The slurry is heated to and 'maintained af a temperature above about 80 C; inal e'lo'sed reaction vessel. An oxygen bearing, oxidizing gas' is fed into'Y the reaction vessell in'- a'mount sufficient tonaritain a partial pressure of oxygen in: the reaction* vessel'.A The reaction is continued to dis-v soliv'e uranium'- v'aflues@ in: the leac'h solution. When uraniumvaluesha've been extracted froml the uranium bear-V iii-g` starting naterial tol therv desired extent, the flow` of oxygen' bearing; oxidiiing' gas to the reaction vessel is stopped and theA slurry is digested in the presence ofv iron sulphide and udis'solved residuev ata temperature abo'v'e atmospheric temperature with -Vagitation until dissolved4 'Y residue and pre-etsiiate-d coppervalues aren separated from The eiect'ive leach solution is* an aqueous acid solution having" a pI-I"y value Within the ran-ge of from about 3 t'o about pH 015. The acid can be formed in situwhen minerali stil'phid'es or elemental sulphur are associated with the uranium bearing material either occurring naturally with the) uranium values or added to the slurry.. Sulphuric acid is. generated in the oxidation of mineral sulphides or elementalsulphur inl aqueous solution. Thus, ,the starting solution can be wateror waterk with a 'minor amount of sulphuricV aci'df to` acL c elerate-the initial acid forming reaction, or `toneutralize basic constituents such ascalcium carbonateV or" magnesium:carbonate which may be'fpresentin the'- uranium' bearingV startingv material,

- When mineralsulphidesorelemental' sulphur areA not associated with theuranium bearing. starting material in amount sulicient-1 to produce andi maintain thedesired aqueous acidV sulphate `solution within? the rangez of' from about pH 0i51 to aboutpH 3;,the desired ac'idconcetration can be obtained byV adding sulphuric acid' to" the slurry.,Y

The metho'dzis;offcourse,.,independent ofl hypothetical considerations' and is based ony results obtained from operations conducted under varying conditions-L Otheruranium minerals sueltas torbernite, metatorbernite,.carnotite; autunite, and-th'elilce have been found to rea'et' with sulphuric acid under oxidizing"conditions` wi'thi resulting? extraction andV dissolution of uranium values.'`

'Wehave-found further that provided iron sulphide, A

-the major portion of the dissolved `copper values canb'e vPatented Mar. il,

How;- ever, the following equationsillustrate the'reactions precipitated by stopping the tlow of oxygen bearing, oxidizing gas to the reaction vessel after the uranium values have been extracted from the starting material to the desired extent and thereafter retaining, or digesting, the slurry for a short period of time with agitation at or about the leaching temperature. Iron sulphides present in the slurry appear to react with dissolved copper values during this digesting period and convert them to and precipitate them as copper sulphite. The precipitation ofcopper values by the iron sulphide can be expressed by the following equations:

These reactions and others having a similar effect appear to be favoured by the relatively high temperature and low acidity conditions which are characteristic of the preferred method of leaching described above. The eX- traction and dissolution of copper values is favoured by high oxygen concentrations and for the best results the oxygen concentration should be maintained as low as possible consistent with a satisfactory leaching rate and eX- traction eiciency of desired uranium values. An oxygen partial pressure of from to 25 pounds per square inch, preferably from 5 to 10 pounds, equivalent to from 5 to 125, or from 25 to 50 pounds, per square inch air pressure is very satisfactory.

Some iron is dissolved in the solution as a result of the copper precipitation reaction, probably in the form of ferrous salts, but it does not interfere with the subsequent treatment of the solution for the recovery of the uranium values.

The following examples illustrate the operation of the method. In accordance with conventional practice, amounts of uranium are referred to as grams per litre U308 or percent U3O8. It is understood, of course, that the uranium need not be present as U3O8 but may exist in other forms, such as in solution as UO2SO4.

Example I A uranium bearing ore containing about 1.17% U308; about 7.3% Cu; about 4.4% Fe; about 4.6% S; about 25% A1203 and about 44.2% Si02 was ground so that about 70% passed through a 200 mesh screen. That is, the particle size was less than 0.0029 inch. A slurry of about 2,000 grams of this ore was formed with water, about 50% solids by weight, and the slurry was charged into an autoclave wherein it was heated with continuous active agitation to and maintained at about 160 C. under a partial pressure of oxygen of about pounds per square inch above the pressure autogenously generated at the temperature at which the reaction was conducted. At the end of a 4 hour leaching period, the pH value of the solution was about 1.8 and the solution contained about 10 grams per litre U3O8; about 23.4 grams per litre Cu;- about 2.0 grams per litre Fe; and aboutSl grams per litre S04. This represented extractions of 93% U3O8, 34% Cu and 37% S. At the end of the 4 hour leaching period, the flow of oxidizing gas Was stopped and the slurry was digested at about 160 C. with active agitation for `about 2 hours. At the end of the digestion period, Undissolved residue was separated from 4the solution by filtration and the resulting solution had a pH value of about 1.3 and contained about 11.2 grams per litre U308; about 6.8 grams per litre Cu; about 12 grams per litre Fe;

and about 5 8 grams per litre S02. The resulting solution represented extractions of about 94% U302; about 43% S and about 10% Cu. About 90% of the copper was retained in the undissolved residue for recovery, if desired, separately as a copper concentrate such as by dotation.

The uranium bearing ore in this example contained suf- Example 2 A uranium bearing material which contained about about 0.56% U302; about 4.4% Cu; about 3.6% Fe; about 3.9% S; about 2.7% CaCO3; about 6.7% MgCO3; about 22.5% A1203; about 45.5% Si02 was ground to about 70% minus 200 mesh screen. About 2,000 grams of this ore was mixed with about 2,000 grams of water to form a slurry. The slurry was heated to and maintained at a temperature of about 160 C. for about 4 hours with active agitation in an autoclave maintained under an oxygen partial pressure of about l0 pounds per square inch. The solution remained at a pH value of about 7, no free acid was present in the Solution and no uranium or copper values were dissolved. The failure of this experiment was attributed to the presence of the relatively large amount of CaCO3 and MgCO3 which consumed the small amount of acid formed in the oxidation f of the iron sulphide.

Example 3 Experiment 2 was repeated with the addition of about 75 grams of sulphuric acid to the original slurry. After 4 hours, the pH value of the solution was reduced to about 2.8 and the solution was found to contain, after separation of the undissolved residue by filtration, about 5.9 grams per litre US02 and about 27.4 grams per litre Cu representing an extraction of about 87% of the U303 and about 43% of Cu from the starting material and dissolved in the solution.

Example 4 Example 2 was repeated with the addition of about 200 grams of pyrite and about 75 grams H2804. The slurry was heated to and maintained at a temperature of about 160 C. with active agitation under an oxygen partial pressure of about 10 pounds per square inch. At the end of a 4 hour leaching period, the pH value of the solution was reduced to about 1.5. The solution contained about 5.8 grams per litre U308 and about 12.7 grams per litre Cu, representing an extraction of about 93% of the uranium and about 27% of the copper. The pyrte apparently reacted with the oxygen to provide additional sulphuric acid which improved the uranium recovery. At the same time, the copper extraction was reduced. At the end of the 4 hour leaching period, the ow of oxygen to the autoclave was stopped and the solution was digested at about 170 C. for about 3 hours. Undissolved residue was separated from the solution by filtration and the resulting solution contained about 6 grams per litre U3Os and about cient iron sulphide in naturally occurring form toA provide allthe acid necessary for the extraction of the uranium values and for the precipitation of dissolved'copper values. v f

0.1 gram per litre Cu representing an extraction of about 91% of the U3O8 and only about 0.3% of the Cu. The undissolved residue was subjected to a conventional totation operation which resulted in the recovery of about 95% of the copper as a concentrate comprising about 10% of the 4original Weight of the uranium-copper bearing starting material. The copper concentrate assayed 40% copper.

One of the important advantages of the present method of separating copper values from uranium values is that copper reports in the solid residue as a sulphide which can be recovered very easily and eiciently as a otation concentrate in ideal condition for the recovery therefrom of copper metal by conventional methods.

The etticiency of the present method is influenced by the acid concentration of the leach solution, the amount of iron sulphide present in the slurry, and the temperature y in the range of from about pH 3 to pH 0.5. When pyrte or pyrrhotite is present in the slurry, the acid concentration of the solution adjusts itself automatically within the a vtenlperature within the range of from about 100 C. to about 200 C. with an oxygen bearing, oxidizing gas, said gas b'eing fed into the reaction vessel in amount sufficient to maintain'a partial pressure of oxygenin the vessel,4

and undissolved residue at a temperature-above atmospheric temperature for a period of time sulicient to precipitate at least a major portion of the' dissolved copper values from the solution, and separating leach solution containing dissolved uranium values from the undissolved residue and precipitated copper values. y

5. The method of recovering uranium valuesY from uranium bearing starting material containing copper values which comprises forming a vslurry comprised of nely divided uranium bearing material containing copper values and an aqueous acid sulphate solution having a pH value within the range of from about pH 3 to about pH 0.5, heating the slurry to and maintaining it ata temperature above about 80 C. in a closed reaction vessel, feeding an onygenbearng, Voxidizing gas into the reaction vessel in'-` amount sucient to maintain a partial pressure of orrygenv in the vessel, continuing the reaction to dissolve uranium'.

` cient to precipitaterat least almajor portion of the dissolved copper values from the solution, and .separating leach solution containing dissolved uranium values from the Vlindissolved residue and precipitated copper values.

-References Cited ntile of this patent A y UNITED STAITE'VSPATENTS 1,098,282 McCoy L-; May 26, 1914 2,662,009V Roberts et al.V Dec. 8, 1953 OTHER REFERENCES `Engineering and Mining Journal, vol. 155, No. 9 (September 17954), pp.v'104l09. 

1. THE METHOD OF RECOVERING VALUES FROM URANIUM BEARING STARTING MATERIAL CONTAINING COPPER VALUES WHICH COMPRISES THE STEPS OF FORMING A SLURRY COPRISED OF FINELY DIVIDED URANIUM BEARING MATERIAL CONTAINING COPPER VALUES, IRON SULPHIDE AND AN AQUEOUS SOLUTION OF THE GROUP CONSISTING OF WATER AND AN AQUEOUS ACID SULPHATE SOLUTION, HEATINGTHE SLURRY TO A TEMPERATURE ABOUVE ABOUT 80*C. IN A CLOSED REACTION VESSEL, FEEDING OXYGEN BEARING. OXIDIZING GAS INTO THE REACTION VESSEL IN AMOUNT SUFFICIENT TO MAINTAIN A PARTIAL PRESSURE OF OXYGEN IN THE VESSLE, CONTINUINGTHE REACTION TO DISSOLVE URANIUM VALUES IN THE LEACH SOLUTION STOPPING THE FLOW OF OXYGEN BEARING, OXIDIZING GAS TO THE REACTION VESSEL, DIGESTING THE SLURRY ON LEACH SOLUTION CONTAINING DISSOLVED METAL VALUES, IRON SULPHIDE AND UNDISSOLVED RESIDUE AT A TAMPERATURE ABOVE ATMOSPHERIC TEMPERATURE FOR A PERIOD OF TIME SUFFICIENT TO PRECIPATE AT LEAST A MAJOR PORTION OF THE DISSOLVED COPPER VALUES FROM THE SOLUTION, AND SEPSRATING LEACH SOLUTION CONTAINING DISSOLVED URANIUM VALUES FROM THE UNDISSOLVED RESIDUE AND PRECIPATED COPPER VALUES. 